Reversible drive for a magnetic recording medium



April 8, 1947. M. cAMRAs 2,418,541

REVERSEIBLE DRIVE FOR A MAGNETI RECORDING MEDIUM Filed Nov. 22, 1943 5sheets-sheet 1 All ul.

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REVERSIBLE DRIVE FOR A MAGNETIC RECORDING MEDIUM Filed Nov. 22, 1943 5Sheets-:Sheet 2 n MARY/U CAME/as" 7 f f f/i 5- April 8, 1947. M. cAMRAs2,418,541

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REVERSIBLE DRIVE FOR A MAGNETIC RECORDING MEDIUM Filed Nov. 22, 1943 5sheets-sheet 4 MAew/u Cfr/viens I l A 5y f f 52225 April s, 1947.

5 sheets-sheet S Filed Nov. 22, 1943 lv/ CN Mnewu -CA Mens Patented Apr.8, 1947 REVERSIBLE DRIVE FOR A MAGNETIC RECORDING MEDIUM Marvin Camras,Chicago, lll., assignor to Armour Research Foundation, Chicago, Ill., acorporation of Illinois Application November 22, 1943, Serial No.511,253

2 Claims. 1

This invention relates to a magnetic recorder, and more particularly toan electromagnetic instrument for recording sound on a paramagnetic wireor tape and reproducing the sound therefrom.

Electromagnetic recording and reproduction of sound vibrations, speech,etc., dates back to the end of the nineteenth century, and While someimprovements and refinements have been made since that time, in both themethod and apparatus, Vsuch improved apparatus and methods have not beenutilized to any great extent commercially. There are a number of reasonsfor this, the most important of which are probably the inherentlimitations in the apparatus heretofore proposed. In general, the volumelevel of the reproduced signals of previous systems was low, thefrequency range covered was very limited, the extraneous noise wasobjectionable and the distortion of the wave forms were often o! suchcharacter and magnitude as to render the reproduction of extremely lowquality and at times almost unintelligible.

In a co-pending application of mine, entitled Method and means ofmagnetic recording, illed December 22, 1941, Serial No. 423,928, nowPatent No. 2,351,004, issued Junee 13, 1944, and assigned to the sameassignee as the present invention, a novel system of magnetic recordingis described and claimed. The present invention is directed to a novelapplication of the method and means described and claimed in saidcopending application, and to a novel combination of elements employedtherewith.

4 This particular application is a division of my co-pending applicationentitled Magnetic recorder, U. S. Serial No. 452,419, filed July 27,1942, now Patent No. 2,351,005, issued June 13, 1944, and assigned tothe same assignee as the present invention.

It is an object of the present invention to provide a novel apparatusfor magnetic recording and reproduction.

A further object of the present invention is to provide a novel unitaryapparatus for magnetic recording and reproduction including a recordinghead, reel means for carrying and moving a paramagnetic Wire or tape tothe recording head, an electric amplier and a loud speaker.

A still further object of the present invention is to provide novelindicating means for indicating the position of, recorded soundvibrations on a paramagnetic wire or tape.

A still further object of the present invention is to provide novelmeans for shifting from a position for magnetic recording to a positionfor magnetic reproduction on a paramagnetic wire or tape.

`.Another and still further object oi the present invention is toprovide novel means for reeling and unreeling a paramagnetic wire ortape in the recording and reproducing apparatus.

Still another object of the present invention is to provide novel meansfor stopping the reels at any desired selected portions of therecordingor reproduction.

Still another object of the present invention is to provije a novelmethod and means for braking the wire carrying reels.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and manner of construction,together with further objects' and advantages thereof, may best beunderstood by reference to the following description, taken inconnection with the accompanying drawings, in which:

Figure 1 is a front viewof one embodiment of the present invention, asviewed in a plane indicated by theline I-I of Figure 2;

Figure 2 is an end sectional view through the apparatus, as taken alongthe line II-II of Figure 1; v

Figure 3 is an irregular sectional view of the apparatus, as taken alongthe line III--III of Figure 2; Y

Figure 4 is a diagrammatic illustration of the control switch and thewire position indicating mechanism;

Figure 5 is a view taken along the line Figure 3;

Figure 6 is a view taken along the line VI-VI of Figure 3; and

Figure '1 is an electric circuit diagram ofthe 1 system.

In Figures 1 to 3 of the drawings, there is illustrated a magneticrecorder and reproducer constructed in accordance with the teachings ofthe present invention. All of the essential component parts of myrecorder and reproducer, with the exception of the microphone and asource of power, are contained in a single unit illustrated. This unit,as illustrated in Figures 1 to 3, includes a housing member I0 having abase Il, a top wall I2 and an inclinedfront panel I3. Thev inclinedfront panel I3 includes a lower portionv 'I4 and an upper portion I5which is offset rearwardly from the lower portion I 4.

A magnetic recording head I6, an erasing head I1, a recording medium I8in the form of a wire, and a pair of reels I9 and 20, are all mounted onthe outer face of the upper panel I on the front wall I3. Reels I9 and28 are mounted for rotation on shafts 2| and 22. When the apparatus isbeing operated as a recorder or reproducer, the reel I9 is the supplyreel and the reel 20 is the receiving or windup reel, the reel 20 beingdriven in a counter-clockwise direction as viewed in Figure l. When thewire is to be rewound onr ment presently to be described which is housedwithin the casing I6 and behind the front panel I3. v

The record medium or wire I8 is preferably vmade of a high carbon steeland, by way of example, may conveniently have a diameter ofapproximately .005 inch. This wire I8 is threaded through the erasinghead I1 which, as will presently be explained. completely demagnetizesthe wire and removes any magnetism therefrom, whether caused fromprevious records made on the wire, or from any extraneous source. Thewire I8 then passes around a guide pulley 23,

' which is mounted for free rotation on the shaft 24, and held in placeby a lock nut 25. 'I'he wire is thereafter passed through the magneticrecording head I6, which will presently be explained in detail. The wireI8, after leaving the recording head-I6, passes around a guide pulley26, which is freely mounted on a shaft 21, and held in'pla'ce by a locknut 28. The wire I8 finally passes to the takeup reel 20. A pair oflevel winding guide nngers 29 and 30 are preferably provided to assurean even distribution of the wire on the reels I9 and 28. K

A motor 3| is provided in the housing Il! and is arranged to beselectively connected to either the shaft 2| or the shaft 22 of thereels I9 and 20, respectively, for driving one reel or the other, asdesired. in a clockwise direction, as viewed in Figure 3. This motor 3|is preferablv mounted in an vinclined position, as shown in Figure 2,with its drive shaft 32 extending substantially perpendicular to thepanel portion I4. The motor 3| may be `conveniently mounted on a bracket33 which is ,secured to the base II, as at 34. and to the motor as at35. As shown in Figure 2, an opening 36 is provided in the base I I intowhich the casing of the motor extends. but does not completely passtherethrough. This opening 36 is provided as a. Ventilating opening.andfacilitates circulation of air around the motor and the amplifyingequipment presently to be described.

Drive pulleys 31 and 38 are mounted on the shafts 2| and 22, which carrythe reels I9 and 20, respectively. It will be noted that the pulley 31is smaller than the pulley 38 in order to increase the rewind speed.

As shown in Figures 2, 3, 5 and 6 of the drawings, the shafts 22 and 2Ipass through the panel portion I5 and then through the skeleton framestructure 39 and 39', respectively; each of which includes a back plate40 and a plurality of spacer plates 4|. These structures 39 and 39 areassociated with each of the shafts 22 and 2| on the rear of the panelportion I5, and contain the mechanism for reciprocating the levelwinding guide ngers 30 and 29. While the structures 39 and 39'associated with the two shafts 22 and 2| are not identical. they arevery similar, and for that reason a detailed description of only one ofthe structures, namely the structure 39 associated with the shaft 22,will be discussed. The structure 39, which is associated with the shaft22 is shown in detail in Figures 5 and 6.

The shaft 22 is mounted in bushings 25| and 252 which are carried,respectively, by the panel portion I 5 and the back plate 49. Formed orattached on the center portion of the shaft 22 is a worm 253. Meshingwith the worm 253 is a worm wheel 254 which is secured to a shaft 255which extends generally downwardly and substantially at right angles toshaft 22. Shaft 255 has formed or secured thereon below the worm wheel254,

a worm 256 which meshes with a worm wheel 251 mounted on a shaft 258which extends substantially at right angles not only to the shaft 22 butalso to the shaft 255. The shaft 258 is mounted on two of the spacermembers 4I on opposite sides of the skeleton structure 39. Mounted onone end of the shaft 258 is a. heartshaped cam 259 which is arranged toengage a cam follower 260 which is in the form of an inverted L-shapedfinger which is secured to a rod 26| which carries the level Winderguide iinger 30. The end of the cam follower 268 projects through a slot262 in the spacer member 4| adjacent the cam 259.

Also connected to the shaft 25-8 is a exible drive cable 42 which drivesthe counter mechanism 43 which indicates the relative position of 4anyportion of the record medium I8 with relevel Winder guide finger 29.' Abiasing spring 265 in the form of a resilient Wire having several turnsinthe center is secured at one end of the back plate 48 of' the skeletonframe `structure 39 associated 'with the shaft 2| as at 266, and issecured at its other end to the end of the link arm 45 as at 261. Thisspring 265 resiliently holds the cam follower 268 against theheartshaped cam 259.

Referring now to Figure 3, a pair of do'g leg levers 46 and 41 arepivotally mounted as at 48 and 49 to a bracket 50 which is secured tothe rear end wall of the motor 3| by attaching bolts 5|. The dog leglevers 46 and 41 each have downwardly projecting legs 52 and 53respectively, on which is pivotally mounted driving pulleys 54 and 55,respectively. Drive pulley 54 is associated and mechanically coupled toa friction roller 56, while drive pulley 55 is associated with andmechanically coupled to a friction roller 51. Fixed to the motor driveshaft 32 is a friction roller 58 against which friction roller 56 andfriction roller 41 are selectively arranged to be moved into drivingcontact. A flexible drive cable 59 extends around drive pulleys 54 and31. A flexible drive cable 60 extends around drive pulleys 55 and 38.

As shown in Figure 3, the friction roller 58 is in driven engagementwith they drive roller 58, and, accordingly, the shaft 2| is beingdriven'by the motor 3|. 'Ihis in turn causes reel I9 to be driven in acounterclockwise direction as viewed in Figure 1, and accordingly thewire I8 is being unwound from the reel 28 and rewound on the' reel I9.When'the friction roller 56 is moved out of engagement with the frictionroller 58 and the friction roller 51 is moved into engagement with thefriction roller 58 the shaft 22 is driven by the motor 3| which in turncauses the reel 28 to be rotated in a counter-clockwise direction, asviewed in Figure 1.

The dog leg levers 46 and" have upwardlyv extending bent leg portions 6|and 62, as is clearly shown in Figures 2 and 3. A ringer 63 extendsbetween the two upstanding legs 6I and 62 and is arranged to be moved bythe motor control operating handle 64. Thearm A6.3 is pivotally mountedon a bracket 65, as at 6-5', which is supported on a frame construction66 mounted on the rearv of the lower panel portion I4. As isdiagrammatically shown in Figure 4, the motor control operating handle64 is pivotally mounted on the subframe member -66 as at 61. The motorcontrol 64 determines Whether the motor is causing the wire I8 to bemoved in a recording and reproducing direction through the recordingheadI6, or whether the motor is causing the wire I8 to be rewoundon reel I9.When the handle 64 is thrown to the right as viewed in Figure 1 ordownwardly as viewed in Figure 4, the wire I8 is moving in a recordingand reproducing direction (i. e., it is being wound up on reel 28). Whenthe handle 64 is thrown to the left as viewed in Figure 1 or upwardly(as shown) in Figure 4, the wire I8 is moving in a rewinding direction(i. e., it is being rewound on reel I9). When the handle 64 is in anintermediate or central position, the wireis stationary and the motor 3|is deenergized. Although not shown, it is to be understood that thehandle 64 operates an electric switch which closes the energizationcircuit of the motor 3| when the handle 64 is moved in either direction.

When the finger 63 is rocked against the upper f leg portion 62 of thedog lever 41 the friction roller 51 is moved out of engagement with thefriction drive roller 58 against the action of the tension spring 68which extends between and is secured to the lower ends of the legportions 52 and 53. Similarly, when the lever 64 is rotated so as tomove the finger 63 against the upper leg portion 6|, the friction rollerA56 is moved away from the friction roller 58 and at the same time thetension spring 68 pulls the friction roller 51 into engagement with thefriction .roller 58. When the riger 63 is in its mid position frictionrollers 56 and 51 fare beth pulled against friction roller 58 by thespring 68. Since these rollers 56 and 51 try to drive the wire I8 inopposite directions, it will at once be apparent that the friction driverolls 56 and 51 of themselves act and serve as a brake for stopping themotor 3| as well as immediately stopping movement of the wire I8.

Also mounted within the housing I8 is the amplifying equipment,generally indicated at 69 in Figure 2. The amplifying equipment 69 ismount` ed to the rear of and around the motor` 3|. A loud speaker 18 ismounted on the lower panel portion I4.

Turning to Figure 1 of the drawings, the left portion of the lower panelI4 contains an opening 1|, which is covered by the cloth lscreen 12,which covers theI open front of the speaker 18.

On the right-hand side of the lower panel .por-

tion I4 are the control knobs and indicating means for the electricalcircuits. Control knob 13 is a volume control; control knob 14 is anon-and-ofl switch, as well as the tone control; and control knob 15determines whether the electrical circuit will operate as a recorder oras a reproducer. To the left of control knob 15 is a red light 16 whichis lit when the control knob 15 is moved to a. Dosition for operatingthe apparatus as a recorder. A green light 11 is located to the right ofthe control knob 15 and is lit when the control knob 15 is moved to aposition for causing the apparatus to operate as a. reproducing unit. Aneon bulb 18 is located above the control knob 15 and, as will presentlybe explained, indicates the proper volume setting when the apparatus isoperated as a recorder.

The motor control 64 is located on the front of the panel portion I4, asshown in Figure 1, While the indicating means 43 is located to the leftthereof.

The electrical circuit of the apparatus is diagrammatcally shown inFigure 7. The electrical circuit in general includes the magneticrecording head and the audio amplier, a loud speaker and microphone plugwhich is `arranged to be connected to any suitable type of microphone.With the switch connections as shown in Figure 7, the apparatus is in aposition for reproducing sound vibrations which have previously beenrecorded on the wire |8. The magnetic recording headV includes a coil 19which is magnetically associated with the wire I8 or, in other words, itis so related to the wire I8 that the lines of flux produced by themagnetized wire will intersect the windings of the coil 19. In thepreferred form of the invention the wire I8 passes ldirectly through thetapered pole portion 88 of a laminated iron core member 8| and through aportion of the coil 19 which surrounds the tapered pole portions 88 andthe air gap therebetween. The coil 19 is connected to theinput gridelectrode 82 of the first audio ampliiier tube 83 through a shieldedconductor 84 (the shield being indicated by the broken lines 85). Theother side of the coil 19 is connected to the cathode 86 of the electrondischarge device 83 through the conductor 81. As is indicated at 88, thecathode 86 and the conductor 81 is grounded. Two switches 89 and 98 areconnected in the circuit of conductor 84. Interposed between the switch98 and the grid electrode 82 is a bias cell 9|. nected through a. highresistance 92 to the grounded Shield 85.

The electron dis'charge'device 83 may 'be of any suitable type for usein an audio amplier and as shown 'is of the multigrid type.- Moreparticularly, the electron discharge device 83, in addition to the inputgrid electrode 82 andthe cathode 86, includes a heating filament 93, ascreen grid electrode 94, a suppresser grid ,electrodel 95 and an anode96. A second stage of amplification is provided by an electron dischargedevice 91 which is connectedby a capacity coupling 98 to the outputcircuit of the electron discharge de- The electron discharge device 91is similar to' the electron dischargedevice 83 andincludes, in additionto the grid electrode |08, a heating filament |8I, a cathode |82, ascreen grid electrode |83, a suppresser grid electrode |85 'and ananode,

|86. The cathode |82 is providedv with avselfbiasing resistor |81 and aby-pass condenser |88Y to maintain the lcathode at the desired'-potential. Y

This cell 9| is con-` 7 The screen grid |03 and the suppresser grid |05are connected to the circuit in the conventional manner, the screen grid|03 being given a suitable positive bias through a circuit presently tobe explained, and connected to ground through the by-pass condenser |09.Y

The anode-cathode circuit of the electron discharge device 91 isprovided with aby-pass condenser lI and a variable tone control resistorIII which are connected between the anode |08 and ground. The anode |06is also connected through a couplingl condenser H2 to the input gridelectrode H3, of an output or power tube ||4. A self-biasing resistorI|5 is connected between the grid electrode ||3and ground,

The output of power tube ||4, in addition to the grid II3, includes afilament II6, a cathode ||1, a screen grid ||8, a suppresser grid I|9and an anode |20. The suppresser grid I I9 is directly connected to thecathode ||1 in the conventional manner, while the screen grid ||8receives a suitable biasing potential, in a manner presently to beexplained. The cathode ||1 is connected through a self-biasing resistor|2| and a parallel connected filter condenser |22 to ground.

In the output circuit of the power amplier tube I|4 is the neon lampcircuit. This neon lamp circuit includes a condenser |23 and a variableresistance element |24, which are connected in series between the anode|20 and the grounded conductor 81. The neon lamp 18 is connected betweenthe grounded conductor 81 and the movable element |25 of the resistor|24 which determines the voltage drop across the neon lamp.

The power amplifier tube ||4 is connected to an output transformer |26.The input winding or primary of the transformer |26 is connected betweenthe anode |20 of the power amplifier tube I|4 and the screen grid I|8 ofthe same tube. The secondary of the transformer |26 has its opposite endconnected to an output jack |21 and a resistance element |28. Anintermediate point |29 on the secondary of the transformer |26 isconnected to the grounded conductor 81 and also to a contact point |30of a switch 3|. A second intermediate point |32 is connected to a secondcontact point |33 of the switch |3I.

A loud speaker |34 is connected through switch |3I on one side to thetapped point |32 on the secondary of the transformer |26, while it isconnected through the separable contact elements |35 and |36 of theoutput jack |21 to the tapped point I 29 on the secondary of thetransformer |26. With the switch I3| in the position shown in Figure 7of the drawing, the speaker |34 is arranged to be energized from theoutput of the ampliiier. 'Conductors |31 and |38 are connected to ashorting switch (not shown), which is arranged to be closed when theunit is being rewound.

Power for the amplier circuit is obtained through a rectitler unit |39which includes a power transformer |40, a rectier tube |4I, and suitablefilter elements presently to be described. The input side of the powertransformer |40 is connected through a plug |42 to a suitable source ofalternating current (not shown), such for example as the conventional110 volt 60 cycle alternating current available in most cities. Anoverload fuse |43 is connected between plug |42 and transformer |40, inone part of the circuit, and an on-oft switch |44 is connected in thecircuit on' the opposite side. The switch |44 is preferably combinedwith the tone control and operated from a single knob 14 (Figure 1).

In addition to a primary winding |45 on the power transformer |40, thereare provided three secondary windings |46, |41 and |48. The secondarywinding |45 is arranged to be connected to the filaments 93, |0| and ||6of the tubes 83, 91 and II4. The arrows associated with winding |48indicate diagrammatically that they are arranged to be connected to thearrows on the iilament elements referred to.

The secondary winding |46 supplies power to the cathode |49 of therectifier tube |4I. Two anodes |50 and |5I are connected to oppositeends of the winding |41. The center point on windings |41 and |48 areboth grounded through a conductor |52. A group of lter condensers |53and |56 are connected in the circuit as shown, while an inductivereactance element |51 is connected in the circuit of the coil |46 andthe cathode |49. Resistance elements |58 and |59 are also provided andare connected vin a conventional manner. It is to be understood that thecircuit arrangement above described is a conventional full waverectifler circuit for supplying the desired potential to the variouselements of the audio amplifier. The desired positive potential foranode 96 and screen grid 94 of tube 83 is obtained through conductor |60and dropping resistors |6| and |62. The desired potential for anode |06and screen gridv |03 of tube 91 is obtained through conductor |63 anddropping resistors |64 and |65. The desired potential for anode |20 andscreen grid ||8 of tube I|4 is obtained through conductor |66, theconductor |66 being connected through the primary winding of the outputtransformer |26 to the anode |20 while being directly connected to thescreen grid I|8.

The red pilot light 16 and the green pilot light 11 are energizeddirectly from the secondary winding |48 of the power transformer, aswitch |61 being arranged to selectively energize either the green pilotlight 11 or the red` pilot light 1,6. As is indicated in Figure 7, thegreen pilot'l light is in a state of energization and, as has previouslybeen mentioned, this indicates that the circuit is arranged to reproducesound vibrations magnetically recorded onthe recording medium I8. Whenthe apparatus hereinbefore described is to be employed for recordingsound vibrations on the record medium I8 a high frequency oscillator isnecessary. Suchan oscillator is diagrammatically illustrated in Figure'1 and includes an electron discharge device or oscillator tube |68which is provided with a filament |69,y a cathode |10, a control gridI1I, a screen grid |12, a suppresser grid |13 and an anode |14. A tunedcircuit including an inductance |15 and ,a parallel connected con'-denser |16 is provided. The inductance |15 and the condenser |16 areconnected at one end to the anode |14 and are connected at their otherend through a condenser 11 to the input grid |1| of the oscillator tube|68. The lower end of the tuned circuit is also connected through aconductor |18, a condenser |19 to a conductor |80, which is connected tothe magnetic head I6 in a manner presently to be explained. A biasresistor |8| is provided between the control grid |1| of tube 68 andcathode |10. The cathode |10 is connected through a condenser |82 to anintermediate point I 83 on inductance |15. This intermediate point |83is arranged to be connected through a switch |84 to the high potentialside of a source of electric energy, as

.l N0. 2,351,004, issued June 13, 1944.

9 supplied through conductor |66. Cathode is also connected through aconductor |85 to the grounded side of an equalizer circuit |86.

The equalizer circuit |86 is a lter circuit including a plurality ofinductance elements |81, a plurality of resistance elements |88 and a.plurality of condensers |89, which are preferably connected together inthe manner shown in the drawings. One end of the equalizer circuit |86is arranged to be connected through a switch |90i to either the groundedconductor 81 or to a conductor |9|. The conductor |9| is connected to acondenser |92 and a conductor |93 to the output circuit of the tube ||4in the manner shown.

It is to be understood that the oscillator |68 and its associatedcircuits are employed only when the equipment is being employed as arecorder. When the equipment is being employed as a reproducer, ashereinbefore described, the oscillator is cut out of the circuit in amanner which will be readily apparent from an inspection of thedrawings. Switches 89, 90, |3|, |61, |84 and |90, as well as a switch|94, which connects the output conductor |80 of the oscillator circuitto the recording head I6, are all arranged to be moved from their fullline position as shown in Figure 7, to their dotted line position asshown in Figure 7 when it is desired to operate the equipment as arecorder rather than as a reproducer. To this end, all of these switches89, 90, |3I, |61, |84, |90 and |94 are all preferably mounted as a gangswitch for operation by the control switch (Figure 1), which controlswitch or lever, as previously described, also controls the direction ofrotation of the reels I9 and 20.

A description of the equipment and its operation as a recorder will nowbe made. Assume that all ofthe switches 89, 90, |3I, |61, |84, |90 and|94 are thrown to their dotted line positions and that the record mediumor wire |8 is moving from right to left, as viewed in Figure '7. Thehigh frequency alternating current flow in the tuned circuit of theoscillator, and particularly in the inductance |15, causes a highfrequency current to be induced in the Winding |95 which is connected tothe erasing coil I1.

Since the wire or recording medium I8 is passing through the erasinghead I1 prior to the time when it reaches the recording head I6, all

previous magnetization of the wire or magnetization resulting from anyextraneous source is removed from the wire I8 immediately prior to thetime it enters the recording head I6.

A microphone is connected through a suitable lead (not shown) to themicrophone plug |96 which forces the movable center contact |91 awayfrom its engagement with its stationary seat |99 and thus causes thevoice energy to be transmitted through switch 90 by a cell 9| to thecontrol grid 82 of the rst tube 83 of the amplifier circuit. The outputof the audio amplifier is connected to the equalizer |86. the conductor|80 and the switch |94 .to the coil 19 of the recording head`|6. Theoutput of the oscillator tube |66 is also fed through a couplingcondenser I 19 to the same input conductor |80 of the recording head I6.This causes a superimposing (as distinct from amodulaton) of the audiofrequency current on the high frequency current generated in theoscillator tube |68.

vided. One contact 200 of the jack |99 is con nected directly to theinput circuit of the second stage of audio amplification as representedby the tube 91. More particularly, the contact 200 is connected to theupper end of the potentiometer 99, which in turn is connected through amovable contact 20|` to the control grid |00 of the tube 91. The othercontact 202 of the jack |99 is connected to the grounded conductor 81through a conductor 203. This arrangement may be conveniently used torecord incoming radio programs or the like directly on the record mediumI6. Since the amplification from the output of a radio, or other similarequipment, is usually considerably greater in intensity than the outputwhich may be obtained from any microphone circuit, the rst stage ofamplification in the audio amplier is skipped, when it is desired torecord an incoming radio program, or the like, by connecting theoutputof the radio (not shown) to the jack |99.

The jack |21, which has previously been described, is provided in theequipment for the purpose of using a separate and larger loud speaker(not shown), if desired, when the equipment is being operated as areproducer.

It will be observed that when the equipment isset for reproduction, theswitch |61 connects the green light 11 to the energizing winding |48 ofthe transformer |40. When the switch |61 is in its dotted line position,as it is placed when the equipment is being operated as a recorder, thered light 16 is connected to the energizing winding |48 of thetransformer |40 `instead of the lamp 11. Y

Associated with the switch arm 64 and the counter mechanism 43 is meansfor automatically moving the switch 64 to its neutral position. Moreparticularly, the shaft 204 extends out of the counter mechanism 43 andcarries on the end thereof a cam cylinder 205 which has a transversegroove 206 therein immediately followed by a transverse raised portion201. An arm 208 is pivotally mounted for movement about the point 209and is spring biased by a coil spring 2|0 for movement in a clockwisedirection, as viewed in Figure 4. The right-hand end of the member 208is provided with a cam engaging portion or protuberance 2|| which ridesin` engagement with the cam cylinder 205. A link member 2 l2 extends tothe inner end yof the switch arm 64 where the inner end of the switcharm 64 engages the forked end 2|3 of the arm 63. The Yconnecting arm 2|2is pivotally mounted to the inner end of the switch arm 64 as at 2|4.The opposite end of the connecting arm 2|2 is bent as at 2|5 to providean abutment surface and again at 2 6 to pro- Vide a second abutmentsurface which is arranged to be engaged by the end 2|1 of the arm 208,as will presently be described.

Th'e cam cylinder 205 is arranged to rotate very slowly so that onerevolution thereof substantially represents the entire linear movementof the wire or record medium I8. More particularly, the transversegroove 206 and the transverse raised portion 201 are arranged to beengaged by the cam follower 2|| just before the wire I8 is completelyunwcund from 'the spool or reel from which the wire is being taken. Whenthe cam follower 2|| drops down into the groove 208 rthe spring 2l0lifts the left-hand portion 211 of the'arm 208 upwardly. as shown in thedrawings, to pull the switch to a neutral position. If the switch armhad been thrown over in the other direction, and the unit was operatingwith the arm in that position. then the abutment portion 2li would be inengagement with the lend 2I1 of the arm 200. When the cam follower 2||strikes the raised portion 201 it will cause the left-hand portion 2l1of the arm 208 to be pressed against the abutment 2li to force theswitch 04 to its neutral position. It will be observed that if the camfollower 2li strikes the groove 2|6 before striking the raised portion201 that the end 2|1 will merely temporarily be lifted oif the abutment2li. but would not cause any movement of the connecting arm 2i2.Continued movement of the cylindrical cam 205, however, would causethecam follower 2li to engage the high portion 201 which would theneffect operation of the connecting arm 2 I2 in the manner just describedto move the switch arm El to vits neutral position. The above describedmechanism is adapted to prevent the wire I8 from being completelyremoved from one of the reels I9 or 20, which would thereafter require arethreading of the mechanism. By suitably locating the groove 20B andthe raised portion 201 in the cylindrical cam 205, it will readily beapparent that a safety mechanism for stopping the apparatus is providedwhen the wire i8 approaches its end on either spool or reel I9 or 20.

The above described mechanism, as will read@ ily be appreciated by thoseskilled in the art, is an extremely compact and rugged equipment forrecording and reproduction of sound vibrations. It has been found inpractice that a relatively small spool or wire, such as may convenientlybe mounted on a small portable unit, will carry sufiicient wire torecord or reproduce continuously for several hours. Much longer periodsof recording and reproducing may be obtained by using larger spools andlonger lengths of wire.

While I have shown a particular embodiment 4 of my invention, it will,of course, be understood that I do not wish to be limited thereto, sincemany modifications may be made and I, therefore, contemplate by theappended claims to cover all such modifications as fall within the truespirit and scope of my invention.

I claim as my invention:

1. In a magnetic recording and reproducing unit, a support including acasing having a panel and a base, a recording and reproducingelectromagnetic head mounted on said panel, a long paramagnetic wire ortape, a pair of reels rotatably mounted on said panel for rotation aboutaxes extending substantially perpendicular to said panel and oniwhichthe ends of said wire l2 or tape are disposed and around which the bulkof said wire or tape is wound, said head being disposed to have saidwire or tape pass therethrough, a motor mounted on said support andhaving a friction driving drum, a pair of levers rockably mounted inproximity to said motor and each having a friction drum to be drivenrotatably mounted thereon, said driven drums being disposed on oppositesides of said driving drum,Y 10 spring means urging said driven drumsinto frictional engagement with lsaid driving drum, control means forselectively moving one or the otherY of said members to move itsassociated driven drum out of engagement with said driving drlmi,

whereby either of said driven drums may be selectively retained indriving engagement with said driving member, and means coupling saiddriven drums to said reels respectively for rotatably driving saidreels.

2. In a magnetic recording unit a supporting structure, a recordingelectromagnetic head mounted on said structure, a long paramagnetic wireor tape, a pair of reels rotatably mounted on said structure and onwhich the ends of said wire or tape are disposed and around which thebulk of said wire or tape is wound, said recording head being disposedin magnetizing relation to said wire or tape, driving means mounted onsaid structure and having a friction drive drum,

a pair of members rockably mounted in proximity to said motor and eachhaving a friction drum rotatably mounted thereon and arranged to bedriven by said driving drum, said driven drums being disposed onopposite sides of said driving drum, means above both of said drivendrums of said driven drums may be selectively retained in drivingengagement with said driving member, and means for transmittingrotational movement of said driven drums to said reels respectively. 5MARVIN CAMRAS.

file of this patent:

UNITED STATES PATENTS Number Name Date 2,089,287 Molloy Aug. 10, 19372,281,793 Patrick May 5, 1942 2,078,357 Woodmansee Apr. 27, 19371,142,384 Tiiany June 8, 1915 1,883,560 Chipman Oct. 18, 1932 2,086,130Hickman July 6, 1937 2,277,305 Clopton Mar. 24, 1942

